Grey-headed Bullfinch

The grey-headed bullfinch, also called Beavan's bullfinch, is a finch widespread across China and also present in Bhutan, north-east India and Taiwan, with a wintering range extending to eastern Burma. Its natural habitats are boreal forest and temperate forest (Wikipedia, general species account).

That short account is the only source read for the Bhutan guide. It gives no plumage, size, diet or breeding information, so none is stated.